Manuel Pellegrini, the Manchester City manager, is to investigate the spate of muscle injuries that threaten to undermine the champions' return to form.

City, who will find out who they play early next year in the first knock-out round of the Champions League today, may have to play through the Christmas programme without a recognised senior striker and their captain after a costly 1-0 victory over Premier League bottom side Leicester on Saturday.

The club's only fit striker, Edin Dzeko, suffered a calf muscle injury in the warm-up before Vincent Kompany pulled up with a recurrence of a hamstring problem late in the second half. Both are unlikely to be fit before the new year and join forwards Sergio Aguero and Stevan Jovetic on the casualty list.

Their absences will leave sizeable gaps at both ends of the field and Pellegrini wants to find out if there is an underlying cause, although the Chilean will not make excuses.

"We must find a reason," said Pellegrini, whose side have won seven games in succession.

"It is very unlucky to have the three strikers out with injuries but we must try to solve the problem and play another way, or keep a clean sheet.

"It is difficult because we have to play a lot of games during the last days of December, but I never complain about the players who cannot play."

Teenage striker Jose Angel Pozo was drafted into the side at the King Power Stadium at the last moment and the lack of current alternatives could force City into the transfer market next month. Pellegrini said: "In January we will see, it is an option. I think our squad must always be strong."

Another looming problem is the loss of Yaya Toure to the African Nations Cup next month.

That is likely to mean Pellegrini will press harder to extend the loan of Frank Lampard. The midfielder again proved City's chief inspiration and was their match-winner at Leicester, scoring the only goal - his sixth for the club - five minutes before half-time. The 36-year-old's loan from sister club New York City expires at the end of the month and Pellegrini wants him to stay longer.

The Leicester manager, Nigel Pearson, feels his side are letting themselves down at both ends of the field.

Defeat left them bottom of the table and without a win in 11 games, since they stunned Manchester United on 21 September.

He said: "It is about being dominant in both boxes and we have not delivered that again."